Ontogenetic shifts in behavior and host-plant preference in the tropical clown grasshopper <i>Homeomastax silvicola</i> (Orthoptera: Eumastacidae)

Members of the genus <i>Homeomastax</i> have been predicted to exhibit contrasting specialization through ontogeny, with a strong preference for fern plants during the nymphal phase. We investigated whether host-plant specificity and use differ between adults and nymphs of the tropical acridid <i>Homeomastax silvicola</i> (Rehn &amp; Rehn, 1934) within a lowland Caribbean reserve in Costa Rica. Host-plant preference (<i>Nephrolepis brownii</i> (Desv.) Hovenkamp &amp; Miyam. vs. other plants) was assessed by counting adults and nymphs in transects differing in <i>N. brownii</i> fern cover. We assessed their vertical positioning in host plants and analyzed their defensive behavior in response to a potential threat. While adults showed no preference for <i>N. brownii</i>, nymphs were highly associated to ferns, being five times more abundant in areas of high <i>N. brownii</i> cover, and 97% of them being found in that host plant. Nymphs occupy lower parts of the plant, gradually ascending to higher parts as they become adults. Notably, experiments demonstrated that nymphs had over three times less probability of escaping from threats than adults. These results suggest that ferns are crucial host plants for the feeding and protection of <i>H. silvicola</i> progeny, which become more generalist as they develop. We posit that describing specialization patterns in tropical fern-grasshopper systems, and ultimately measuring the drivers of these patterns, offers valuable insights into understanding intraspecific variations of interactions through ontogeny.